1. Field of the Invention
This invention relates to digital signal processing and more particularly relates to digital signal processing to mitigate signal asymmetry.
2. Description of the Related Art
During the read process in a data storage device, a read head is typically passed over a data record in order to convert pre-recorded data into an analog signal. For example, in a magnetic tape drive, a magneto-resistive read head (“MRRH”) is passed over a data record that has been previously written as flux reversals on a magnetic tape. As the MRRH is passed over the tape, the MRRH converts the flux reversals into an electrical analog signal that represents the data originally stored on the magnetic tape. An analog to digital converter (“ADC”) periodically samples the analog signal and converts the sampled analog signal to a digital input signal. The ADC typically samples and converts a plurality of digital input signals forming a digital waveform. A data storage device such as a magnetic media storage device processes the digital waveform to reconstruct the data that was originally written to the tape.
The data waveform is typically recorded as flux reversals on a magnetic media and is symmetric, such that if the MRRH was perfectly adjusted, the received analog signal would be symmetric about a known reference level. For example, the analog signal may be symmetric about a reference level of zero volts (0 V). Unfortunately, manufacturing inconsistencies and read head wear may cause the read head to generate an asymmetric analog signal from the magnetic media. The asymmetric analog signal is converted to a plurality of digital input signals forming an asymmetric digital waveform. The asymmetry in the digital waveform increases the probability that the data storage device will interpret the asymmetric digital input signal incorrectly, resulting in an increased number of data errors.
Data errors due to a read head generating an asymmetric analog signal may make the read head unsuitable for shipment in a magnetic media storage device, increasing the failure rate and manufacturing costs of the read head. In addition, as the read head wears over time, the analog signals generated by these worn read heads will become more asymmetric. This shortens the life of the read head and the data storage device, increases the probability of an uncorrectable read error, and increases warranty costs.
From the foregoing discussion, it should be apparent that a need exists for an apparatus, system, and method that mitigates the asymmetry of a digital input signal waveform generated from an asymmetric analog signal. Beneficially, such an apparatus, system, and method would reduce the manufacturing defect rate and adapt the mitigation of the asymmetry over the life of the read head and storage system in order to compensate for changes in the read head with time.